When you buy an R Pubsure Pro pack, you get credits in your R Pubsure account. Credits essentially mean how many manuscripts you can upload and get checked on the R Pubsure platform. For example, for the 70$ package, you get 2 credits and for the 135$ package, you get 6 credits. When you upload a paper, you use a credit.
UPDATE as on 1st Dec '20.
We have recently launched new plans due to which the credit system ceases to exist. However, all those who have previously bought credits shall continue to have them in their accounts until they are fully consumed. After which, new plans shall be applicable to them.